1. Field of the Invention
This invention relates to the shape and configuration of the attack face and cutting edge structures of a saw tooth, and particularly to such structures applied to a four-sided rotatable saw tooth for a wood cutting saw.
2. Discussion of the Prior Art
Four-sided rotatable teeth for circular tree cutting saw blades in which one edge of the tooth is positioned radially outermost from the rotary axis of the blade to cut a kerf in a standing tree are known from U.S. Pat. No. 4,932,447. This type of tooth has a four-sided head with an attack face at one end, each side being coterminous with the attack face along a cutting edge. The tooth is oriented on the blade with one of the sides on the outside of the blade so that the one side and its cutting edge are substantially vertical in the cutting position of the blade, as the blade is advanced through a tree. The outside cutting edge forms the kerf by chiseling off the working (vertical) surface of the kerf, and chips from the cutting operation flow along the attack face of the tooth for evacuation from the kerf. When the outside edge becomes dull, the tooth is rotated 90.degree. or 180.degree. about its longitudinal axis and resecured to present one of its other three edges in the outermost position for cutting. When all four edges have become dull, the tooth is replaced or reconditioned.
In this orientation of the tooth on the blade, two of the sides of the tooth are in a substantially horizontal plane, one of the horizontal sides being on the top side of the tooth and the other horizontal side being on the bottom side of the tooth. The top side of the tooth is in close proximity or contact with the top side of the kerf (on the tree trunk) and the bottom side of the tooth is in close proximity or contact with the lower side of the kerf (on the top of the stump). This close proximity or contact results in a certain amount of wear along the top side edge and bottom side edge of the tooth during a cutting operation, although most wear occurs at the outermost side of the tooth which actually cuts the kerf.
Adjacent sides and the attack face of saw teeth meet at the corner tips of the attack face. Because the mass of material of the tooth diminishes toward a corner tip and because abrasion occurs along both of the cutting edges which define a corner tip between the outermost edge and the top and bottom edges, wear is most concentrated at the corner tips of the tooth. Wear of the corner tips is especially exacerbated under sandy conditions of cutting, as occurs frequently in the southeastern part of the United States where sand on the forest floor can get into the bark of the trees, e.g. from wind or rain, and abrade teeth severely or where trees are severed at ground level. In addition, because the corner tips are at the extremities of the leading or attack face of the tooth, they are especially susceptible to damage from impact, for example, from hitting a rock or another piece of equipment.
It has been known to retard wear in all types of saw teeth under these conditions by providing one or more tungsten carbide plates to cover the high wear areas of the attack face. However, this is only a partial solution to the problem, as the corners still wear more quickly than the inner edges of the attack face, even when the corners and the inner edges are carbide. In addition, the carbide plates in prior teeth have typically had sharp points or tips, which wore or broke off relatively easily.